1. Field of the Invention
This invention relates to a color chart creating method for creating color charts for use in color correction of an inkjet printer, and to a color correcting method.
2. Description of the Related Art
In a printing system which carries out digital color printing, a different color definition is used for each of a display device such as a liquid crystal display for displaying images, a scanner for reading images, and a printing machine for performing printing. A color management for controlling printing colors of the printing machine is carried out by putting such different color definition for each digital device to a color conversion among one another using ICC profiles. The ICC profiles are files of formats specified by the International Color Consortium, and are files defining characteristics of the color spaces of devices.
A color printing machine performs printing, using the four color materials of cyan (C), magenta (M), yellow (Y) and black (K) which are generally called process colors. An inkjet printer includes inkjet heads for the respective colors, each head having a plurality of nozzles for discharging ink. When carrying out color printing with such inkjet printer, color charts are printed for use in color correction. Such a color chart has, arranged thereon, a plurality of color patches combining ink color types and dot size types (see Japanese Unexamined Patent Publication No. 2012-164044, for example).
Each color patch on the printed color chart is measured with a colorimetric machine, and ICC profiles are created based on the results obtained.
With a conventional inkjet printer, a limit is set to a total amount of inks due to restrictions of various conditions such as characteristics of inks and water absorption characteristics of a printing medium. The total amount of inks, when the process colors are the four colors of CMYK, is a sum total of the inks of CMYK superimposed for each pixel, which is also called a TAC (Total Area Coverage) value. The inkjet printer therefore has a color reproduction range (color gamut) variable with a limiting value represented by the TAC value (see Japanese Unexamined Patent Publication No. 2004-349980, for example).
In the inkjet printer, the printing medium is transported by rollers. The printing surface of the printing medium contacts the rollers, whereby the ink is transferred to the rollers, and further the ink is transferred from the rollers back to the printing medium, thereby causing a problem of tinting prints. Therefore, the limiting TAC value is set low to prevent the ink transfer to the rollers due to insufficient drying of the ink.
On the other hand, there are various types of inks and printing media used in inkjet printers. While the drying performance of inks depends on the amount of inks applied to a print medium, this drying performance varies with the compositions of the inks.
Therefore, when the limiting TAC value is set low as conventionally done in order to prevent the ink transfer to the rollers due to insufficient drying of the inks, there will arise a problem that the color chart has a color gamut reduced in size. Further, when color correction is carried out based on the color chart with a small color gamut, there will arise a problem that the resulting coloring on prints is different from what is intended.